Feral pigs in north-western Australia: basic biology, bait consumption, and the efficacy of 1080 baits

Abstract

Bait consumption, and the efficacy of 1080-treated grain, were determined for feral pigs (Sus scrofa) during the dry season in the Fitzroy River region of north-western Australia. There were an estimated 250 pigs on the study site (15 000-ha paddock with beef cattle) before poison-baiting, and group size and the basic biology of these pigs were similar to that found elsewhere in Australia. All animals at the study site were naive to the test baits. Fermented wheat with added blood and bone was an attractant for feral pigs but added fish oil was not. Wheat and malted barley were the 'preferred' baits. Lupins and pig pellets were consumed in lesser amounts, suggesting that they are less/not acceptable to some feral pigs. Consequently, the efficacy of 1080-treated wheat and malted barley was determined (n = 3 sites per treatment). Three independent measures of pig activity/abundance were used. The daily sighting index before and after poison-baiting suggested that pig numbers were decreased by at least 81-100% (mean 89%) regardless of which bait was used. The take of both 1080-bait and non-toxic fermented wheat added to each station generally ceased within 1-3 days, and little take occurred during the post-poisoning follow-up. Pig tracks decreased to zero within 1-3 days of poisoning on the two sites where track plots were established. However, due to the arrival of 'immigrant' pigs ~6 days after poisoning on two sites, and the need to close down a third site before poison-baiting could be completed, we believe the absolute efficacy was greater than the 89% overall reduction. Even though they had access to bait, there was no bait-take by non-target species, either native (toxic and non-toxic bait) or domestic (non-toxic bait). The 61 pig carcases found after poisoning were within 20-610 m of active bait stations (mean 232 m), and most were found in clustered groups. These findings are discussed with respect to the development of management strategies for reducing the impacts of feral pigs, and in terms of their potential implications for developing wildlife disease (exotic and endemic) contingency plans.

Feral swine damage and damage management in forested ecosystems

“…This research was subsequently augmented by studies on free-ranging feral swine, including bait uptake and consumption studies (McIlroy et al, 1993;Choquenot and Lukins, 1996), compound 1080 intake , risk assessments to non-target animals (McIlroy, 1992;Twigg et al, 2005a), the effectiveness of ground baiting campaigns with compound 1080 (Hone and Pedersen, 1980;Hone, 1983;Twigg et al, 2005b;Cowled et al, 2006a;Twigg et al, 2006Twigg et al, , 2007 and warfarin McIlroy and Saillard, 1989;Saunders et al, 1990;Choquenot et al, 1990), and the effectiveness of aerial baiting campaigns (Mitchell, 1998;Fleming et al, 2000). Compound 1080 and warfarin have also been used to eradicate feral swine from Santiago Island in the Galá pagos archipelago, Ecuador (Coblentz and Baber, 1987;Cruz et al, 2005).…”

Reduced efficacy of baiting programs for invasive species: some mechanisms and management implications

“…There is also the potential for non-target species to ingest vomitus and therefore be exposed to poisoning, a reasonable consideration given the large 1080 doses in feral pig baits. However, it should be noted that vomiting has not been commonly recorded in studies of 1080 baiting of free-ranging feral pigs (Twigg et al 2005), which suggests that there may be differences between caged and field experiments in the amount of bait consumed while in traps compared with their natural diet.…”

“…Pen trials investigating the toxicity of 1080 to feral pigs observed high rates of vomiting in individuals that ingested 1080, and some pigs that vomited survived very high 1080 doses (Hone and Kleba 1984), which has raised concerns that sublethal dosing due to vomit responses can possibly lead to subsequent aversion (McIlroy 1983;O'Brien et al 1986). However, additional trials, more closely simulating field conditions, demonstrated that while vomiting frequently occurred in feral pigs poisoned with 1080, it does not improve their survival as sufficient fluoroacetate had been absorbed before emesis (O'Brien 1988;O'Brien and Lukins 1988;Twigg et al 2005). Similarly, the mortality of fat-tailed dunnarts (Sminthopsis crassicaudata) offered meat containing an estimated LD 90 of 1080 was only one-tenth of that in animals orally administered the same dose in water, presumably due to vomiting (Sinclair and Bird 1984).…”

“…While the amount of 1080 in vomitus is likely to be similar to that of the bait itself , relatively small amounts of this material (,50 g) are likely to occur in the environment (Twigg et al 2005). There is also the potential for non-target species to ingest vomitus and therefore be exposed to poisoning, a reasonable consideration given the large 1080 doses in feral pig baits.…”

Attractants for wild pigs: current use, availability, needs, and future potential

“…Adequate prebaiting is essential for success, and at least 3-6 days are needed to concentrate and accustom wild pigs to new food sources (Linhart et al 1993;Campbell et al 2011;Twigg et al 2005). Further, it is recommended that bait stations be established and supplied for 3-7 days prior to incorporating any bioactive agent (Linhart et al 1993).…”